Fix macOS transcription hotkey reliability

[basnijholt]

Summary

• debounce the macOS transcription hotkey so repeated skhd key-down events cannot immediately start and stop recording
• keep transcription hotkey diagnostics in cache logs instead of discarding stderr
• patch skhd.app during macOS hotkey setup with a microphone usage description, re-sign it, reset stale TCC grants, and re-register the service when needed
• document the Accessibility and Microphone permission requirements

Verification

• bash -n scripts/macos-hotkeys/toggle-transcription.sh scripts/setup-macos-hotkeys.sh scripts/macos-hotkeys/toggle-autocorrect.sh scripts/macos-hotkeys/toggle-voice-edit.sh
• uv run ruff check agent_cli/install/hotkeys.py
• uv run pytest tests/install/test_extras.py tests/test_requires_extras.py -q
• stubbed debounce smoke test with NOTIFIER=/usr/bin/true and AGENT_CLI=/usr/bin/true